1. Field of the Invention
The present invention relates generally to rotary drill bits of the Zublin type and more particularly to the cutting structures utilized on these types of bits.
2. Description of the Prior Art
There are various types of rotary drill bits in the well drilling art. One type is the drag bit which comprises a solid head having abrasive cutting elements mounted thereon. As the head is rotated within the bore hole, the cutting elements scrape over the surface of the well formation to remove portions thereof. Drilling fluid is circulated into the well bore to remove the cuttings scraped away by the cutting elements. Conventionally, diamonds have been utilized as the cutting elements mounted on the head, although synthetic diamonds have been used recently.
Another type of rotary drill bit utilized in the well drilling art is the rolling cone type rock bit. Such a bit usually comprises a main bit body having a plurality of legs extending downwardly therefrom. A cone cutter is rotatively mounted on a journal extending radially inward from each of the legs. Each cone cutter has a plurality of tungsten carbide inserts mounted thereon. As the bit is rotated, the cone cutters roll on the bottom face of the bore hole, with the inserts contacting and disintegrating the earth formation. Circulated drilling fluid is also used in these types of bits to remove the cuttings chipped away by the insert elements.
A third type of rotary drill bit is the Zublin type bit in which a cutter is rotatively mounted on an inclined journal pin carried eccentrically by a stem. Instead of rolling on the bore hole face, this eccentricity enables the cutter to travel in a tortuous path in which the cutting elements on the cutter dig away at the bottom of the hole with a combined chipping and scraping action.
Early Zublin type rotary bits exemplified in U.S. Pat. Nos. 1,784,476; 1,859,948; and 1,945,240 had cutting teeth formed on the cone cutter, similar to the milled tooth rolling cone type bits of today. Recently, Zublin type rotary bits have been made with tungsten carbide inserts mounted on the cutters. These bits are described in patents such as the Russian Pat. No. 187,697.